Smoking is linked to working hours, according to new research which found that people who work longer smoke more.

People who work long hours find it harder to quit smoking, and those who have given up are more at risk of starting again, researchers said.

The study by researchers at the Loughborough University found direct links between the hours worked and the number of cigarettes smoked, finding that people who work longer smoke more.

The study, which used data from the British Household Panel Survey, reviewed the smoking behaviour of more than 20,000 people over a 19-year period.

It found a smoker who increases their working week from 40 to 60-plus hours is less than half as likely to quit smoking as someone who stays on a 40-hour week.

"We were interested to find out what happens to smoking behaviour as working hours change, and have identified a clear link between the hours worked and an individual's likelihood of smoking," said Professor Andy Charlwood from the School of Business and Economics, who led the study.

"When smokers increase their hours above a typical 40 hour working week, the chances they will successfully give up smoking fall, and they become progressively less likely to give up as their working hours increase," said Charlwood.

"Former smokers who start working longer hours are also more likely to relapse," he said.

"Even if people like their jobs and choose to work long hours, we tend to experience more stress and less pleasure at work than we do when undertaking most other day to day activities.

"Because smokers experience smoking as a pleasurable and stress relieving activity, the additional stress of working long hours is likely to increase the craving for cigarettes," said Charlwood.